Description

Coomassie R-250 and G-250 dyes are two chemical forms of a disulfonated triphenylmethane compound that is commonly used as the basis of stains for detection of proteins in gel electrophoresis and Bradford-type assay reagents for protein quantitation. The R-250 (red-tinted) form lacks two methyl groups that are present in the G-250 (green-tinted) form, which is also called colloidal coomassie dye. Typically, coomassie gel stains and protein assay reagents are formulated as very acidic solutions in 25 to 50% methanol. In acidic conditions, the dye binds to proteins primarily through basic amino acids (primarily arginine, lysine and histidine), and the number of coomassie dye ligands bound to each protein molecule is approximately proportional to the number of positive charges found on the protein. Protein-binding causes the dye to change from reddish-brown to bright blue (absorption maximum equals 595nm).

Highlights:

Easy detection – Develops intensely colored complexes with proteins

High sensitivity – Can determine as little as 0.5μg/cm2 of protein present in a gel matrix

Reversible staining – Anion of Coomassie Brilliant Blue formed in the acidic staining medium combines with the protonated amino groups of proteins by electrostatic interaction; resulting complex is reversible under the proper conditions

Differentiation between bound and unbound dye – When dissolved in 0.01M citrate buffer at pH 3.0, has an absorption maximum at 555nm; protein-dye complex is characterized by a peak slightly broader than that of the free dye with a maximum at 549nm

Chemical properties of Coomassie Blue R:

Name: Coomassie Brilliant Blue R-250

Formula: C45H44N3NaO7S2 (sodium salt)

CAS number: 6104-59-2

Molecular weight: 825.97

Solubility: essentially insoluble in water; dissolve first in methanol

Chemical properties of Coomassie Blue G:

Name: Coomassie Brilliant Blue G-250 (colloidal)

Formula: C47H48N3NaO7S2 (sodium salt)

CAS number: 6104-58-1

Molecular weight: 854.02

Solubility: slightly soluble in water; best to dissolve first in methanol or ethanol